The present invention relates to a dose reading device for a fluorescent glass dosimeter detecting the intensity of fluorescence generated upon excitation by ultraviolet light, and more particularly, to a dose reading device having an improved fluorescence reading system for a multiplicity of fluorescent glass elements accommodated in a magazine. Furthermore, the present invention relates to a magazine capable of accommodating a multiplicity of fluorescent glass elements which generate fluorescence upon excitation by ultraviolet light, and more particularly, to a dose reading magazine and a method of manufacture for same, whereby the fluorescence can be read off while the aforementioned elements are accommodated in the magazine. Moreover, the present invention relates to a dose reading magazine, dose reading method and dose reading device, whereby reading of high doses can be performed. Furthermore, the present invention also relates to a dose reading device whereby the weak fluorescence from compact fluorescent glass elements is gathered efficiently, and hence detection sensitivity is improved.
In the installation and operation of facilities such as nuclear reactors, accelerators, X-ray generators, and radio isotopes, it is necessary to achieve complete safety in radiation management, in order to protect human beings from radioactivity. In particular, management must be provided to ensure that the radiation dose to which the employees working in various fields in the aforementioned facilities, and the users of the facilities, are exposed comes within a prescribed tolerance range. Dosimeters are used for radiation management of this kind. These dosimeters are located in prescribed locations within a facility, and/or are carried by employees and users, and by reading out the respective exposure doses thereof at regular intervals, it is possible to manage the radiation doses to which employees and users are exposed.
One type of generally used dosimeter is a fluorescent glass dosimeter. In general, a fluorescent glass dosimeter uses glass elements made from phosphate glass containing silver ions. After being irradiated with radiation and activated, these glass elements generate a phenomenon (radio photo luminescence:RPL) whereby they produce fluorescence when excited by ultraviolet radiation of wavelength 300-400 nm. Since the intensity of the fluorescence produced is directly proportional to the radiation exposure dose received by the relevant glass element, it is possible to measure the radiation exposure dose by detecting the intensity of the fluorescence. A particular feature of fluorescent glass dosimeters of this kind is that they can be read out repeatedly, without the core which generates RPL being destroyed by the reading operation.
In measurement using a fluorescent glass dosimeter of this kind, the light emitted by the ultraviolet excitation light source is passed through an optical filter to selectively extract ultraviolet light of prescribed wavelengths, and is then incident on one face of the fluorescent glass elements. The fluorescent light consequently generated by the fluorescent glass dosimeter is passed through an optical filter to selectively transmit light in a prescribed wavelength range, whereupon it is opto-electrically converted by an photomultiplier tube to obtain an electrical signal having a level that is roughly proportional to the fluorescence intensity, and the fluorescence intensity, and hence the radiation exposure dose is measured from the level of the electrical signal.
In general, as illustrated in FIG. 27, a dose reading device for reading out the radiation exposure dose according to the principles described above uses a magazine 3 accommodating a multiplicity of capsules 1 holding a fluorescent glass element 2 therein. This magazine 3 is loaded onto a magazine conveying device 4 by a magazine supply device (not illustrated), and conveyed to a prescribed position. The fluorescent glass elements 2 are then extracted, one by one, from their respective capsules 1, by means of an extracting device (not illustrated), conveyed to a fluorescence detection position which is shielded from external light, and then are subjected to ultraviolet irradiation and fluorescence quantity detection.
However, a conventional dose reading device as described above involves the following kinds of problems. Specifically, since the fluorescent glass elements accommodated in the magazine must be taken out from the magazine, one by one, and transported to a reading position, in order to perform fluorescence reading, a large amount of time is required to read out the fluorescence quantity of a multiplicity of fluorescent glass elements.
Furthermore, during extraction of the individual fluorescent glass elements from the magazine, or during conveyance thereof, transportation problems may occur, such as the elements catching on surrounding members, or the like. In particular, since the small-sized fluorescent glass elements, described hereinafter, are simple glass elements and do not have a metal frame, or the like, then if a transportation problem arises during loading thereof into a conventional reading device, there is a very high risk of problems such as breaking of the glass, soiling of the surfaces thereof, or degradation of the fluorescence-based measurement accuracy due to the presence of foreign matter.
Furthermore, since a mechanism is required for extracting the fluorescent glass elements individually, there are drawbacks in that the manufacturing costs rise and the size of the overall device increases. In particular, in a dose reading system using small-sized fluorescent glass dosimeters, as used in diagnostic and medical dose evaluation, animal experiment dose evaluation, and various other types of experiments, and the like, since the fluorescent glass elements are very small, they are extremely difficult to extract mechanically.
Moreover, as described above, a dose reading device generally uses a magazine 3 accommodating a multiplicity of fluorescent glass elements 2 held in capsules 1, as illustrated in FIG. 27 and FIG. 28. This magazine 3 is loaded from a magazine supply device (not illustrated) onto a magazine conveying device 4 and conveyed to a prescribed position, where the fluorescent glass elements 2 are extracted from their respective capsules 1, one at a time, by an extracting device (not illustrated), and then conveyed to a fluorescence detection position which is shielded from external light, where they are subjected to ultraviolet irradiation and fluorescence quantity detection. From the viewpoint of moldability, PS (polystyrene), for example, is used as the material for this magazine 3.
However, since the fluorescent glass elements accommodated in a conventional dose reading magazine of the kind described above must be taken out from the magazine, one by one, and transported to a fluorescent reading position, in order to perform fluorescence reading, a large amount of time is required to read out the fluorescence quantity of a multiplicity of fluorescent glass elements.
Furthermore, during extraction of the individual fluorescent glass elements from the magazine, or during conveyance thereof, transportation problems may occur, such as the elements catching on surrounding members, or the like. In particular, since the small-sized fluorescent glass elements, described hereinafter, are simple glass elements and do not have a metal frame, or the like, then if a transportation problem arises during loading thereof into a conventional reading device, there is a very high risk of problems such as breaking of the glass, soiling of the surfaces thereof, or degradation of the fluorescence-based measurement accuracy due to the presence of foreign matter.
Furthermore, since a mechanism is required for extracting the fluorescent glass elements individually, there are drawbacks in that the manufacturing costs rise and the size of the overall device increases. In particular, in a dose reading system using small-sized fluorescent glass dosimeters, as used in diagnostic and medical dose evaluation, animal experiment dose evaluation, and various other types of experiments, and the like, since the fluorescent glass elements are extremely small, they are extremely difficult to extract mechanically.
In recent years, small-sized fluorescent glass dosimeters have been used in dose evaluation for radiation therapy and diagnosis, dose measurement in animal experiments, precise dose distribution measurement and other various types of experiments, and the like. In measurement using small-sized fluorescent glass dosimeters of this kind, at high radiation exposures of 2 Gy or above, coloration of the fluorescent core in the fluorescent glass element occurs, thereby causing an ultraviolet absorbing action, and hence the exciting ultraviolet radiation required to generate fluorescence becomes attenuated inside the fluorescent glass elements. Consequently, fluorescence readings of 2 Gy or above are corrected by means of a linear correction equation.
However, in a dose reading method for conventional fluorescent glass dosimeters, as described above, if the exposure reaches 10 Gy or above, then there is marked attenuation of the exciting ultraviolet radiation and moreover, if the exposure reaches 100 Gy or above, then the amount of fluorescence conversely begins to decline. Therefore, it becomes impossible to perform correction by means of a linear correction equation, and hence it becomes difficult to measure radiation exposure doses accurately.
Furthermore, the fluorescent glass elements used in a small-sized fluorescent glass dosimeter as described above are extremely small in size. Therefore, the volume thereof which can be excited by the ultraviolet radiation is small, the incident light to the photomultiplier tube is small, and hence adequate sensitivity cannot be obtained when using a fluorescence reading device similar to the prior art.
In this case, since the light receiving surface of the photomultiplier tube, which forms the fluorescence detecting element, is greater than the fluorescent glass element, it is conceivable to adopt means for ensuring the quantity of incident light by shortening the distance between the fluorescent glass element and the photomultiplier tube. However, by shortening the distance between the fluorescent glass element X and the photomultiplier tube 51, the angle of the fluorescent light incident on the photomultiplier tube 51 is increased, as illustrated in FIG. 29. Therefore, when an interference filter 54 is inserted between the fluorescent glass element X and the photomultiplier tube 51, the amount of fluorescent light incident obliquely on the interference filter 54 is increased, and hence the transmission wavelength of the interference filter 54 is shifted to a shorter wavelength and the original selected transmission characteristics cannot be obtained.
The present invention has been devised in order to solve the aforementioned problems of the prior art, a first object thereof being to provide a dose reading device capable of making accurate dose readings while fluorescent glass elements are accommodated in a magazine.
A second object of the present invention is to provide a dose reading magazine and method of manufacturing same, whereby dose reading can be performed while fluorescent glass elements are accommodated in the magazine.
A third object of the present invention is to provide a high dose reading magazine, high dose reading method, and high dose reading device, whereby linear correction can be performed even in the case of high exposure doses, and hence radiation exposure doses can be read accurately.
A fourth object of the present invention is to provide a dose reading device whereby high detection sensitivity can be achieved by condensing weak light from a small-sized fluorescent glass element.
In order to achieve the first object, the present invention provides a dose reading device having an irradiating means for irradiating ultraviolet light forming an excitation light source for a fluorescent glass element, and a detecting means for detecting a radiation exposure dose from the intensity of fluorescence generated by said fluorescent glass element, comprising: a magazine conveying section for conveying a magazine capable of accommodating a plurality of fluorescent glass elements to the position of a fluorescence detecting part for fluorescence detection by said detecting means; and a dark box section for accommodating said magazine conveying section and said fluorescence detecting part.
According to this dose reading device, since the magazine conveying section is located inside the dark box section along with the fluorescence detecting part, it becomes possible to perform ultraviolet irradiation and fluorescence quantity reading while the fluorescent glass elements are accommodated inside the magazine, and hence there is no requirement for devices or labor to extract the fluorescent glass elements from the magazine.
In order to achieve the second object, the present invention provides a dose reading magazine having loading sections capable of loading a plurality of fluorescent glass elements for reading a radiation exposure dose from the intensity of fluorescence generated upon irradiation of ultraviolet light, comprising: an aperture window, which is provided in a prescribed position of said magazine, for allowing the fluorescence generated by said fluorescent glass elements to exit therethrough.
According to this aspect of the present invention, since the fluorescence generated by the fluorescent glass element when it is excited by irradiation of ultraviolet light while in a loaded state in the loading section is emitted via an aperture window to fluorescence detecting means, it is possible to read the radiation exposure dose without taking out the fluorescent glass elements from the magazine. Consequently, no time is taken in the reading task and conveyance problems can also be prevented.
In order to achieve the third object, the present invention provides a dose reading magazine capable of loading a fluorescent glass element which generates fluorescence corresponding to the radiation exposure dose thereof, upon irradiation of ultraviolet light, comprising: an apertures for allowing only fluorescence from an end portion of said fluorescent glass element on the side of incidence of the ultraviolet light to exit therethrough.
According to this dose reading magazine, since it is possible to read only the fluorescence from the end portion of the fluorescent glass element on the side of incidence of the ultraviolet light, where there is relatively little attenuation of the excitation ultraviolet light, then even at radiation doses of 100 Gy and above, there is no inverse decline in the amount of fluorescence. In other words, the amount of fluorescence does not reach a maximum value, but rather keeps increasing steadily, and hence correction by means of a linear correction formula can be performed, and even high doses of 100 Gy and above can be measured.
In order to achieve the fourth object, the present invention provides a dose reading device having a detecting means for detecting the radiation exposure dose of a fluorescent glass element on the basis of the intensity of the fluorescence generated by the fluorescent glass element when irradiated with ultraviolet light, comprising: a condensing means, which is provided between the fluorescent glass element under detection and said detecting means, for condensing the fluorescence generated by said fluorescent glass element.
According to this dose reading device, even if the fluorescence generated by the small-sized fluorescent glass element is very weak, since it is condensed by the condensing means, sufficient incident light to the detecting means is guaranteed, and hence high detection sensitivity can be obtained.